A tire using silica as a reinforcing agent for a tread rubber instead of carbon black has been proposed in order to enhance a low fuel consumption performance of automobiles and to promote reduction of exhaust gas. Such a tire exhibits an excellent wet grip performance since the hysteresis loss on a low temperature side is maintained high. Moreover, the rolling resistance is reduced since a hysteresis loss on a high temperature side is low. Therefore, the tire has the advantage that both a low rolling resistance performance and a wet grip performance are achieved. However, silica brings about increase in electric resistance of a tire since it has a high electric insulation. Thus, silica causes a variety of electric malfunctions. For example, radio disturbance such as radio noise may take place owing to accumulation of static electricity in a vehicle.
Thus, in order to prevent such accumulation of static electricity, there is proposed for example a structure as shown in FIG. 8 wherein a tread rubber “a” comprises a tread rubber body “b” made of an insulating rubber material having a high silica content and an under tread “c” made of a conductive rubber material having a high carbon content and disposed radially inward of the tread rubber body “b”, and to the under tread “c” is connected a terminal portion “d” which extends through the tread rubber body “b” to a tread ground contact surface “as” to become exposed there (see for example Patent Literature 1). In this structure, static electricity in a vehicle is discharged from the terminal portion “d” to a road surface through a rim “R”, a bead portion, a skin rubber (i.e., clinch rubber “g1” and sidewall rubber “g2”) forming an outer surface of a sidewall portion, and the under tread “c”.
Patent Literature 1: JP-A-11-180108